In the practice of opthamology and retinology, the ability to graphically view a patient's retinal area under varying conditions is extremely beneficial in the clinical diagnosis of various disorders. One type of such camera, the fundus camera, is a three-axis camera providing photographic recording of a diversity of recognized fundus presentation modes. The system also provides for black and white digital image recording, editing and archiving. Using highly corrected optical systems, brilliant imaging and high resolution is provided at the base of the retina suitable for clinical diagnosis. Most current cameras are also able to provide documentation of findings through photographic equipment, electronic image sensors and other options.
Fundus cameras are provided with a main black and white camera unit mounted at the bottom camera port. During diagnosis, the clinician may use the main camera to compile a series of images for later diagnosis and documentation, and such activity is a mainstay feature of such units. The main camera is operated from a joystick used to universally position the optics relative to the patient by depressing an actuator button at the top thereof. In such mode, the fundus camera optics and shutter system are activated for a predetermined time interval. When a signal to the fundus camera is received, the flash unit is activated to properly expose the film. If a signal is not received in such time interval, the fundus shutter system closes preventing image capture.
Oftentimes, it is desirable to supplement the black and white photographs with color photographs to enhance the diagnosis and documentation. Accordingly, the fundus camera is provided with a second camera port for the mounting and operation of a mechanical color camera. The operator can interface the color camera with the fundus camera through a connector harness for actuating the color camera from the joystick button. The system is effective in obtaining color exposures for subsequent development, printing and review. This can result is a significant time interval between examination and review of the color photographs.
With the advent of digital color cameras, there has been a pronounced interest at the clinical level to inter-face a digital color camera with the fundus camera. Such a combination would provide high quality, readily available color photographs for concurrent evaluation and diagnosis at the time of examination, as well as electronic storage for documentation and archiving. While widely accepted for many photographic purposes, the integration with the fundus camera has posed substantial problems, which heretofore have prevented effective use in the clinical practice.
Initial digital color cameras incorporated a mechanical electrical contact at the shutter that interfaced with a timing circuit of the flash unit to coordinate the flash sequence at the fully open shutter positions of both cameras. Certain difficulties were apparently created by the proprietary circuitry operating at the flash unit interface. The digital camera appears to incorporate a circuit board that requires a warmup interval before the shutter activation system on the digital camera can be operated. In ordinary usage, this is accommodated at an intermediate shutter button position wherein the circuit board is enabled, the shutter conditioned for release and the focusing system activated. In the fundus camera, the joystick button effectively bypasses the intermediate position. Accordingly, the signal to the flash unit is subject to two preconditions; the circuit warmup time and the mechanical shutter transit time. These two intervals exceed the aforementioned time interval for the fundus flash unit and the fundus shutter system closes before image capture.
The foregoing digital interface problem has been exacerbated by electronic digital cameras that have substantially replaced the mechanical versions. The latter version appears to have replaced the mechanical shutter contact with a non-publicly available electronic package. In normal operation, the mechanical shutter actuation button has two distinct, sequential positions to capture the images. In the first, partially depressed position, the main circuits are powered, the shutter is released for actuation, and the self-focusing mechanism initiated. In the second, fully depressed position, the shutter is released. The flash circuitry includes a delay to initiate the flash at the fully open shutter condition. For most applications, quality digitized images may be captured and archived.
Nonetheless, integration of the electronic digital color camera with the fundus camera has presented difficulties beyond those experienced with the mechanical version. In the fundus camera, the joystick release button is a two-position switch that bypasses the aforementioned three-position sequential button on the camera body. When interfaced, the apparent circuitry of the camera does not synchronize the flash with the shutter, generally capturing an image in the partially opened shutter condition. This appears to result from an inherent circuitry warm up time required prior to the shutter opening sequence. Manual actuation with the internal switch, fast or slow, provides sufficient staging time to allow the circuitry to operate in synchronization whereas the fundus camera sequence results in a time lag at the shutter unacceptably affecting the resultant image. Moreover, the problem of not resetting the flash unit persists. The flash units used in fundus cameras typically require fill discharge and voltage interruption to allow the power supply to reset for the next exposure. The circuitry, the details of which are not publicly available, employed in such electronic digital cameras appear to provide a sufficient residual voltage preventing the flash unit from resetting. In order to make this interface operable, the operator would have to toggle the power supply at the main switch for recycling the flash unit. Understandably, such manipulation is undesirable and laborious inasmuch as a typical examination entails a substantial number of images for capture.
Notwithstanding the foregoing problems, the desire and need at the clinician level to secure high quality digital color images on the fundus camera persists.
Accordingly, it is an object of the present invention to provide an interface between a fundus camera and a digital color camera for providing proper exposure of desired images.
Another object of the present invention is to provide an interface between a fundus camera and a digital color camera flash control that will effect resetting of the fundus camera flash unit after each exposure.
A further object is to provide synchronization between shutter opening on a digital color camera and the flash unit of a fundus camera.
A still further object is to provide a synchronizing interface between a fundus camera and an electronic digital color camera not requiring structural modification of either camera.
Yet another object is to coordinate the shutter systems of a digital color camera and a fundus camera to provide a quality focused exposure in synchronization with the flash unit on a fundus camera.